Discharge tube



P 1936- e. JOBST' ET AL DI S CHARGE TUBE Filed Feb. 6, 1933 "INVENTOR6007/6 68 J03 /lA/S 0770 50055167507 ATTORNEY Patented Sept. 15, 1936UNITED STATES P TEnTcrFicE DISCHARGE TUBE GuntherJobst and Hans OttoRoosenstein, Berlin, Germany, assignors to Telefunken Gesellschaft furDrahtlose Telegraphic -m. b. H., :Berlin,

Germallmazcorporation of Germany hpplicationFebruaryfi, 1933 Serial No.655,354

Jn-"GermanyJanuary 30, .1932

.3 Claims. (01. 250-20) out unduly .much distortion ibeing incidentallyoccasioned.

ln the past it has never beensufiicientlyztaken 'intoconsideration .thatwhen working at different points of the characteristic, :insidetheworking range, the distortion lrnustibe :constant; on the contrary,inithe 'c'asezoi the tub'esrheretofore employedfthe distortion atisometpoirits was :dispro- 'portionately -'.higher than tat'iothertpoints inside the operating range.

,2 Rectifier arrangementsmare also :known .in :the

:art whose rectifying characteristic :.obeys .a logarithmic law andwhich have :the rproperty that the reproducinglintensityeof modulationis independentof Ithe:mean of the radio frequency in- 5 -deed,dependent'upon only the degree of modulationsof'the earrierwave. Circuitschemes'of this kind, inter .alia, :provide for'the use of tubes "whosestatic characteristics obey in some definite manner a logarithmic law in"such a way that 0 from .a definite grid biasing potential the dis-:charge current grows in accordance with a logarithmic law. Acharacteristic of this kind presupposes, as shown in Fig. :1, a curvewhich presents a COIICENitYrtOWQJLdS thegrid-voltage axis 35 (abscissaaxis) .whichoften is designated as a COIIVGX curve Since with decreasingcurrents no adherence close to the abscissa 'axis takes place as ispeculiar to all thermionic discharge actions 'itis hard to realize thesame even in approximation. The invention discloses a ftype of tubesuited 4 both -for radio frequency amplification as well as radiofrequency rectifier Work whose characteris'tic'is so chosen that, entireone hand, if the grid biasing .potential isproperly chosen, it in-.sures volume control attended .throughout the entire range ofregulation with only small cons'tant distortions so that'the quality ofreproductionremains constant throughout'the entire con- .trol range; .onthe other'hand, realization of such a characteristic is readily.feasible with simple 55 means, for instance, variable 'lzmu. Screengrid type tubes will be used 'most suitably inasmuch as in theseamplification is insurable without plate reaction so that it is directlyproportional to the rslope or mutual conductance .of the tube for allpoints. The characteristic .of altube ace .5 cording to this invention,inside the working range, obeys likewise a logarithmic law, thoughbeingconvex inreferenceto the-abscissa axis;

Fig. 2 shows a characteristic curve approximating curves of actual tubesand also corresponding l0 to the function i =-A"log egrld where A is analways positive constant. 'The voltage fed to the grid is 5 'Cgo-I-Cgsin t where ego is the grid biasing potential and e ns the amplitude ofthe radio frequency wave-train.

What should be taken intoconsideration :in this connection is thenecessity of a negative sign of the log. which manifests itseliibyarconvex'curv'a' ture toward the abscissa axis as required according towhat has "been pointed outabove.

Introducingin the value for egrid the current function, then: I

as-a logt o-ego-et sin t) or if .e' is placed outside the brackets, thisequa- Now, if ego, the biasing potential, be so 'setthat its valuebecomes-proportional to theamplitude of the radio frequency, then onbasis of the requirementthat; V

this formula is found I V 40 =-A log egio) A'log (lei-c sin t) include aquantity'being a function of the-variations in the input oscillations.italic-chosen You inside certain limits, is representable by a char-- 1the presupposed acteristic which comes close to negative logarithmiclaw.

In Fig. 3 the function is represented with its differential quotients.The

significance of quantities A, a, and b can be seen with sufiicientclearness from Fig. 3. They are governedv by the conditions ofmaximumslope S (mutual conductance) andthe. size of the range ofmodulation 2=Zmax. in such a way that fies... (2 =sm.... (2 4...) b,+a.

Put ting again a= e,,+ e, sin t there becomes where a substantially isfixed by the maximum slope (mutualconductance) obtainable for 2:0.

e further can be fixed.so that, with adequate dis-' tribution a smallenough distortion will be obtained. However, there is one condition thatimposes alimitatio-n upon 0, namely as follows: The grid voltage, 1. e.,the sum total of grid biasing potential and grid alternating potentialshould never ;extend beyond z=0 towards the right-hand side lest dampingbe caused'by the incipient grid current, and because the presupposedlaw,as will be noted, no longer holds true outside the regulating range,that is to say,'when z 0. An additional condition therefore ise,,,+e,2o." V Combiningthis equation with the last equation,

' this formula follows: 7 p

" whichafter a few transformations results in this value for 0 k i e, e,min.

V In other words, the value of the output currents is governed by thesmallest still controllable grid alternating potential and the quantitya. he so much larger, the .larger 19, and it may become 0 will equal tounity for sufiiciently large lgmjn. or for incoming oscillations.

a=c. Or, if in the equation the explicit value for a is introduced therefollows:

c max e min. 8 min +(Z max.) 8 min. max. 6 min.

e, min. 5 min. e m1n.+Z max. m

-Upon;the side of the output currents of such an arrangement limitationsare imposed which are determined by the lowest occurring amplitude 1mmby the regulation range Z max. and regulability (a max.:6 min).

The characteristic thus fixed is realizable between z =0 and z=zmax. Thenon-realizable points, that is, to the right of 2:0 and left of z=zmx.,since they are located outside the working range, deserve no interest sofar as the working of the characteristic is concerned. Whatever may be:the shape of the characteristics in that range; the operation of thetube will thereby never be impaired. i 7

Under practicaliconditions, it is permissible to deviatejinside certainlimits, from the given negative logarithmic law without causing anmoidental impairment of the effect or result. These deviations suitablyare referred to the deviations 'of the first diiferential quotients, thecharacteristic, which represent the slope and thus the amplification ofthe tube. Departures in the value of 50% of the differential quotient,inside the working'range covering the rangebetween 0 to say -20 V gridbiasing potential, from the law as presupposed, in. other words, slopeinside 50% and thus volume discrepancies at a ratio of not over.

1-:2 will be admissible for all practical requirements.

Fig. 4 shows a circuit arrangement in which a tube according to thisinvention has in its grid circuit a voltage proportional to'the inputamplitude of the oscillations to be received.

A designates the antenna, E the input circuit of the radio frequencytube H whose control electrode is impressed at Q with the amplitudes ofthe G denotes the audion in Whose output circuit is indicated thereproducer device T. By way of a separate rectifier circuit B, aftersuitable amplification, there is obtained a current resulting in thebiasing voltage of the amplifier tube H.

' 'What we claim is: i

1. In a radio receiver provided with a radio frequency'am'plifier stagehaving a tuned input circuit, an electron discharge tube in said'stagehaving a control grid potential-plate current characteristic which islogarithmic over a range of -control grid potentials extending to atleast 20 volts, a vacuum tube rectifier for developing, a

biasing potential for the control grid .of said amplifier which isproportional to the carrier ampli- "tude, of received signal waves, saidbiasing potential being developed across a resistor which is connectedin series in thegrid circuit of said am plifier and also in series inthe plate circuit of said rectifier.

2. In a radio receiver provided with a radio frequency amplifier and. adetector, an automatic volume control arrangement for maintaining thesignal input to the detector substantially constant regardless of fadingof received signal waves, said arrangement including a rectifier tubeprovided with a resistor in its output circuit to develop a negativebiasing voltage for the amplifier signal grid which is proportional tothe amplitude of the signal Waves, means for applying said biasingvoltage tosaid signal grid, said amplifier being provided with a tubehaving a grid voltage-plate current characteristic such that the platecurrent varies as the log of the grid voltage over a relatively widerange of negative grid voltages.

3. An arrangement for amplifying radio frequency currents comprising thecombination of an electron discharge tube having a cathode, a controlgrid, an anode and a screen grid located between said anode and controlgrid, an input circuit connected to said control grid and cathode, anoutput circuit connected to said anode, means for impressing modulatedsignal currents on said input circuit and means for varying the biasvoltage of said control grid, the elements within said tube beingconstructed so that i --.4 log e wherein A is a positive constanti9p=value of plate current ey=value of signal voltage applied to grid.

GUNTHER JOBST. HANS OTTO'ROOSENSTEIN.

